Castor Oyl and his friend Ham Gravy are planning to go out fortune hunting
on Dice Island, but having no seamanship skills, they went down to the docks
to hire an experienced sailor to take them there. There they found Popeye,
a one-eyed sailor with bloated arms and a large chin. He took them on their
adventure, and continued to spend time in their company afterwards, falling
in love with Olive Oyl, Castor's sister. It turned out that Popeye could
become superhumanly strong whenever he ate spinach, which along with his
sense of loyalty and justice, made him a handy guy to have around. His greatest
rival is Bluto, who seeks to win Olive's affections.

Comments: Popeye was created by Elzie Crizler Segar as a throwaway
character to appear in Thimble Theatre, but soon proved so popular that he
took over the strip from its original denizens, the Oyl family. Gradually
the Oyl's were phased out, except for Olive, who had won the role of leading
lady to the bizarre looking hero.

Initially Popeye had no powers, though he was tough, strong
and a good brawler. He seemingly gained his powers during his trip to Dice
Island with his Castor Oyl. Visiting a casino on the island, Castor brought
along Bernice the Whiffle Hen, an African Escape Hen that Castor had been
given by his uncle, because it was reputed that stroking its feathers gave
good luck. Winning millions, the pair tried to leave, but the casino's vengeful
owner, Fadewell, sent his underling, Jack Snork, after them. Snork shot Popeye
multiple times, but, by continually stroking Bernice, Popeye survived; it
seems stroking Bernice granted him his powers, though arguably Popeye might
have always had regenerative powers and superhuman strength without knowing
it.

Popeye started to appear in cartoons produced by the Fleischer Studios in
1932, and it was these cartoons which introduced spinach to his mythos; the
cartoons also turned Bluto, who had been only a minor, one-shot villain in
the comic strip up to this point, into a major antagonist. Popeye made it
on to television in the early 1950's, where he was voiced by both William
Costello and Jack Mercer. He also started appearing in comic books as well
as comic strips.

In 1980 Robin
Williams played Popeye for a big screen musical movie version made by Paramount
Pictures.

DC Comics paid homage to (or ripped off, depending on your point of view)
Popeye in Action Comics #421 when they introduced a strangely familiar character,
Captain Strong, who gained his superhuman
strength by the regular eating of the miracle food sauncha.

Thanks to Paul Entrekin for informing me of Popeye's nephews.

CLARIFICATIONS: Not to be confused with

Captain Strong, a DC Comics character who
bears a strong resemblance to him.